So I've got a 97 SC1 with misfire at idle and corresponding P0303 code. I've replaced the spark plugs, which did seem to help a little, but so far that's all I've done. The misfire goes away as RPM increases, and the code will even clear on its own on a ~1 hr highway drive, but then returns after I've been stopped at a few lights. That leads me to suspect it's a vacuum leak (my logic being that if it was a spark or fuel issue would only get worse with RPM/load, and if it was a temp sensor issue it wouldn't affect only cyl 3).

But just to rule out ignition related issues, my noob questions:
- Are cylinders are numbered from pass side to driver's side, or vice versa? (Is cyl 1 or cyl 4 closest to the passenger tire)?
- Both plugs connected to a given coil fire simultaneously (one of the 2 being waste spark), correct? In other words, I should be able to swap wires between terminals on the same coil in order to rule out an issue with a coil itself? I suspect one or both of my coils have been changed, so the labeling on them may be what's confusing me here.

I think if I can rule out ignition, my next steps will be to:
- Verify the engine temp that the ecu is seeing to make sure it's not a t-stat or temp sensor issue
- Spray starting fluid around the intake manifold/cyl head to try and find a vacuum leak
- Compression test
- Swap injectors between 2 and 3 to see if the misfire moves

Anything I'm missing here?

...'97 SC1 Auto - Shaturn

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But just to rule out ignition related issues, my noob questions:
- Are cylinders are numbered from pass side to driver's side . . .? (Is cyl 1 . . . closest to the passenger tire)?

Yes. If you are standing in front of the engine compartment and looking at the engine, plugs are 1-4 from left to right.

don't recall if they are numbered on the sticker on the radiator support or not

Quote:

- Both plugs connected to a given coil fire simultaneously (one of the 2 being waste spark), correct? In other words, I should be able to swap wires between terminals on the same coil in order to rule out an issue with a coil itself?

clever, can't think of why this woldnt work other than length of plugs

People that don't know better swap the plug wires around all the time then wonder why it's misfiring...
They have a 'polarity', a stronger primary fire and a weaker secondary fire. The secondary generally isn't strong enough to do a proper burn so the PCM responds as if it's misfiring (because it is).

All the vacuum lines come directly off the top of the throttle body, should be easy to spray carb cleaner around and find a leak, if one exists.

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Sparks travel better through a vacuum than through dense air. On a 2 cylinder waste spark system, the cylinder on the compression stroke has dense air and the one on exhaust stroke does not. So, you don't get balanced current flow out of the two secondary ends of the coil, and the controls can detect if you are firing #2 or #4 for example.

People that don't know better swap the plug wires around all the time then wonder why it's misfiring...
They have a 'polarity', a stronger primary fire and a weaker secondary fire. The secondary generally isn't strong enough to do a proper burn so the PCM responds as if it's misfiring (because it is).

Hope this doesn't confuse the OP but I did run a slightly modified '96 SC2 with the wires flipped around with 0 issue's. My dad had a bunch of '94 Cavi Z24 parts, I figured the coils might be more powerful than the S-Series (3.1 V6 vs 1.9 I4), but the catch was the polarity of them is the reverse of the S-Series so instead of the right 4123 order I used 1432. Didn't have any misfires, but the butt dyno said 0hp gain which was rather boring and not according to plan

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Well, that's interesting! Even if 0 gains, it's good to know for replacement if S series coils become hard to find in the future. I've never had a coil issue, but it seems like s series in JYs are slowly dwindling. hasn't been a 3rd gen coupe in my local yard for a while

Almost forgot . . . for OP, rather than switching wires, you could swap the coils and see if the problem goes with the coil

If the Saturn Coupe uses a fragile plastic intake manifold gasket like the Saturn SL1, then that's probably it or will eventually be the cause of misfires. There are some things that just should not be made of plastic.

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